NUCLEAR PLANT OPERATOR MAKES CASE FOR RESTART

SoCal Edison executives want to run one reactor at 70% to lessen tube vibrations

The operator of the San Onofre Nuclear Generating Station presented its case Friday for restarting one of two reactors that have been sidelined since January because of damage to steam generator tubing that serves as a crucial barrier to radiation.

Addressing a panel of federal nuclear safety regulators, a trio of Southern California Edison executives described how reducing power at the reactor to the 70 percent level would dampen destructive tube vibrations caused by pockets of dry, high-velocity steam.

Lowering power would replicate safe conditions in steam generators at other plants, Edison told regulators in front of hundreds of people at a public meeting in Laguna Hills, 15 miles north of the idled plant.

Edison does not have a timetable for the partial restart, and more public meetings are anticipated. The reactors have been offline since Jan. 31, when a tube in Unit 3 developed a leak.

Restarting the Unit 2 reactor, if approved by the Nuclear Regulatory Commission, would test the resilience of two replacement steam generators that were designed to last decades but displayed rapid wear after about 20 months in service. Generators in the Unit 3 reactor have been set aside with more substantial damage after less than a year in service.

After plugging and reinforcing damaged generator tubing, Edison is proposing to restart the reactor at reduced power for five months before performing a new round of inspections.

In written filings with the Nuclear Regulatory Commission, Edison has described the five-month restart and inspections as “interim compensatory actions.” The utility said it “has established a project team to develop and implement a long term plan for repairing the steam generators.”

To help with that long-term solution, Edison would install new monitoring equipment and diagnostic software during the proposed partial-power restart. The plans also call for improved vibration detection equipment and a temporary radiation detection system in Unit 2’s nonradioactive steam lines.

San Onofre has provided about 20 percent of San Diego County’s power needs.

The manufacturer of the generators, Mitsubishi Heavy Industries, did not participate in the meeting.

In studying the problems at San Onofre, Edison said it assembled a team of consultants and experts including Mitsubishi and competing generator makers Westinghouse, Areva and B&W Canada.

Much of the wear on tubing in Unit 2 has been traced to contact with support structures. Edison officials, however, have focused much of their analysis on addressing the cause of tubes rubbing against each other, even though only two tubes in Unit 2 displayed that type of wear.

“It has not been seen before domestically in the industry or internationally, this tube to tube wear,” said Tom Palmisano, vice president of engineering at Edison.

He and Chief Nuclear Officer Peter Dietrich said Mitsubishi incorporated design elements at San Onofre that had worked successfully at several other reactors abroad and in the U.S. — but on smaller generators.